1. Field of the Invention
The present invention relates to a fluid cylinder for driving a die applied to a die-casting or injection machine or the like, and more particularly to a cylinder apparatus that pulls a piston rod with a strong force at the time of opening a die, and operates quickly at other stages.
2. Description of the Related Art
In a die-cast machine or an injection machine, at the stage at which a die is set into a cavity and closed, there is generally a need for quick movement, but no need for a large driving force, while at the stage of opening a die, at the initial, short step of peeling the die away from the product during cooling, there is a need for a large driving force. However, once the die is peeled away to the open condition, there is a need for quick retraction of the die, similar to the case of the step in which the die is set.
Seen from the cylinder side, in the above-noted steps there is a need for quick drive at the step in which the piston rod is extended, and a need for a large driving force at the initial step of pulling in the piston rod after it is extended, after which there is a need for quick retraction.
With respect to the need for the above-described functional requirements, cylinder apparatuses having a variety of constructions have been developed in the past, an exemplary one being that of Japanese Patent No. 2623075, granted for a "fluid cylinder."
This fluid cylinder is shown in FIG. 13 of the accompanying drawings, and is described as "fluid cylinder comprising a cylinder casing 113 having its interior formed with a main cylinder chamber 111 and a pressure intensifying cylinder chamber 112; a main piston 117, slidably housed in said main cylinder chamber 111 and provided with a piston rod 114 linked to a load on its front edge side, for sectioning said main cylinder chamber 111 into a front main cylinder subchamber 115 positioned on the front side and a rear main cylinder subchamber 116 positioned on the rear side; a front supply/discharge path 118, formed within said cylinder casing 113, for supplying a fluid to said front main cylinder subchamber 115; a rear supply/discharge path 119, formed within said cylinder casing 113, for supplying the fluid to said rear main cylinder subchamber 116; and a pressure intensifying piston 123, slidably housed in said pressure intensifying cylinder chamber 112, for sectioning said pressure intensifying cylinder chamber 112 into first and second pressure intensifying cylinder subchambers 120 and 121 positioned on one side but shut off from each other in terms of a fluidity and an other-side pressure intensifying cylinder subchamber 122 positioned on the other side, wherein said first pressure intensifying cylinder subchamber 120 is connected to said front main cylinder subchamber 115, said second pressure intensifying cylinder subchamber 121 is connected to said rear supply/discharge path 119, said other-side pressure intensifying cylinder subchamber 122 is connected to said front supply/discharge path 118, a large fluid force acting backward is imparted to said main piston 117 by guiding a high pressure generated in said first pressure intensifying cylinder subchamber 120 to said front main cylinder subchamber 115 with a movement of said pressure intensifying piston 123 toward one side when the fluid is supplied from said front supply/discharge path 118 to said other-side pressure intensifying cylinder subchamber 122, and said pressure intensifying piston 123 is, on the other hand, moved up to an other-side limit in advance of said main piston 117 when the fluid is supplied from said rear supply/discharge path 119 to said rear main cylinder subchamber 116 and said second pressure intensifying cylinder subchamber 121."
While it is difficult to comprehend from the above-noted basic constitution alone, with regard to, as recited in a dependent claim, the pressure intensifying piston 123 must be interpreted as "being constructed of a cylindrical portion 124 and a disc member 125 having its outer periphery integrally linked to the inner periphery of the other edge portion of said cylindrical portion, said first pressure intensifying cylinder subchamber 120 is, at the same time, disposed in a face-to-face position with one edge surface of said cylindrical portion 124, said second pressure intensifying cylinder subchamber 121 is disposed in a face-to-face position with one edge surface of said disc member 125, said other-side pressure intensifying cylinder subchamber 122 is disposed in a face-to-face position with the other edge surface of said disc member 125, and said cylindrical portion 124 is, further, slidably fitted to the outer portion of said main piston 117.
The first pressure intensifying cylinder subchamber 120 and front main cylinder subchamber 115 are connected by forming a path within the main piston 117, and a valve 126 is provided midway in the rear supply/discharge path 119, when the rear supply/discharge path 119 or front supply/discharge path 118 is at a set pressure, receives this pressure and opens, and which is closed when both the supply/discharge paths 118 and 119 are at a low pressure, the closed valve 126 causing fluid locking of the rear main cylinder subchamber 116, thereby limiting the movement of the main piston 117.
Referring to the patent publication, the operation of the above-noted fluid cylinder is as follows. (Because this application omits the drawings that illustrate the operation steps described below, it is recommended that the drawings in the cited patent publication be referred to as the following description is read.)
First, the main piston 117 (referring collectively to the large-diameter piston 127 and the small-diameter piston 128) is at the forward limit, the large-diameter piston 127 being in contact with the bottom part of the first cylinder tube 113a, and the small-diameter piston 128 being stopped in contact with the stopper 129 of the large-diameter piston 127, with the pressure intensifying piston 123 is at the rear limit, stopped in contact with the rear cover 130.
At this stage, because the front supply/discharge path 118 and the rear supply/discharge path 119 are both connected to a tank and at a low pressure, the spools 131 and 132 are impelled by the springs 133 and 134, so that they are pressed up against the respective valve seats, so that the front valve 135 and the rear valve 126 are in the closed condition.
Therefore, the front main cylinder subchamber 115, the other-side pressure intensifying subchamber 122, and the rear main cylinder subchamber 116 are in the fluid locked condition, thereby fluidly limiting the movement of the main piston 117 and the pressure intensifying piston 123.
At this stage, the piston rod closes the die at the extension limit, and the piston rod 114 is fixed because of the above-noted fluid locked condition.
Next, when a selection valve connects the front supply/discharge path 118 to the fluid source and connects the rear supply/discharge path 119 to the tank, fluid at the set pressure at the fluid source side is supplied from the front supply/discharge path 118 via the second connection passageway 136 to the other-side cylinder subchamber 122, so that the pressure intensifying piston 123 is moved forward by the fluid pressure.
When this occurs, because the surface area of other side of the pressure intensifying piston 123 that receives the fluid pressure within the other-side pressure intensifying cylinder subchamber 122 (total surface area of the cylindrical portion 124 and the disc member 125) is quite a bit larger than the surface area of on the other side of the pressure intensifying piston 123 that receives the fluid pressure within the first pressure intensifying cylinder subchamber 120 (surface area of the cylindrical portion 124), the fluid within the first pressure intensifying cylinder subchamber 120 is compressed, so that a pressure considerably greater than the set pressure is developed.
The high-pressure fluid generated within the first pressure intensifying cylinder subchamber 120 is guided into the front main cylinder subchamber 115 via the first connection passageway 137, thereby applying a large fluid force that causes the main piston 117 to retract. Therefore, the large-diameter piston 127 and the small-diameter 128 that form the main piston 117 are moved rearward by a strong fluid force.
As a result, the die linked to the piston rod 114 is peeled away from the product by a large force, and opened.
When the above occurs, the fluid of the set pressure supplied to the front supply/discharge path 118 presses the spool 131 of the front value 135 so as to place the valve 135 in the open condition.
Additionally, the fluid of the set pressure is supplied via the front supply/discharge path 118, the second connection passageway 137, and the rear pilot passageway 138 to the pilot cylinder chamber 139, thereby pressing the pilot rod 140 of the pilot piston (82) so as to push in the spool 132, thereby opening the rear valve 126.
Therefore, fluid that flows out to the damper passageway (39) from the second pressure intensifying cylinder subchamber 121 and rear main cylinder subchamber 116 is discharged into the tank via the rear supply/discharge path 119.
In the above-noted condition, even if the pressure intensifying piston 123 moves to the forward limit, so that the front edge of its cylindrical part 124 stops in contact with the protruding part 141 of the cylinder casing 113, the large-diameter piston 127 and small-diameter piston 128 that form the main piston 117 continue to move rearward, so that the protruding part 142 of the large-diameter piston 127 makes contact with the protruding part 141 of the cylinder casing 113, thereby stopping its movement.
However, the small-diameter piston 128 is pressed by the fluid flowing into the large-diameter piston 127, and therefore continues to retract, until it makes contact with the stopper 143 provided at the rear part of the large-diameter piston 127 and stops.
When this occurs, pressure-receiving surface area of the small-diameter piston 127 is small and this piston moves at a higher speed than in the condition in which it was moving in concert with the large-diameter piston 127, so that it pulls in the piston rod 114 in a short period of time, thereby quickly lifting up the released die.
As noted above, the small-diameter piston 128 moves to the rear limit and stops, at which point the selection valve operates, so as to connect the rear supply/discharge path 119 to the tank, thereby causing the supply of fluid to stop, the result being that front valve 135 and the rear valve 126 are placed in the closed condition.
To extend the piston rod 114 and close the die, the switching valves are switched over, thereby connecting the front supply/discharge path 118 the tank and the rear supply/discharge path 119 to the fluid source.
As a result, the fluid from the fluid source is supplied via the rear supply/discharge path 119 and the damper passageway 144 to the rear main cylinder subchamber 116 and the second pressure intensifying cylinder subchamber 121 while pressing open the rear opening/closing valve 126, the fluid force acts to drive the main piston 117 forward, and fluid force acts so as to cause the pressure intensifying piston 123 to retract. When this occurs, a load is applied, this being the die having some weight linked to the main piston 117 via the piston rod 114. However, because no load is applied to the pressure-intensifying piston 123, the pressure-intensifying piston 123 moves to the other side in advance.
Further, at this moment, the fluid from the fluid source flows into the head-side subchamber of the pilot cylinder chamber 146 via the front pilot passageway 145, thereby opening the front opening/closing valve 135. As a result, the pressure intensifying piston 123 retracts, whereby a part of the fluid flowing into the second connection passageway 136 from the other-side pressure intensifying cylinder subchamber 122 then flows into the first pressure intensifying cylinder subchamber 120 via the front supply/discharge path 118, the front main cylinder subchamber 115 and the first connection passageway 137, the remainder of the fluid being discharged to the tank via the front supply/discharge path 118.
Subsequently the pressure intensifying piston 123 moves up to the other-side limit and comes into contact with the rear cover 130, at which the main piston 117 starts moving forward. Because of the relationship of contact surface areas, the small-diameter piston 128 moves first, and because the small-diameter piston 128 has a smaller area receiving pressure, it moves at a higher speed.
Then, when the small-diameter piston 128 comes into contact wit the stopper 129 of the large-diameter piston 127, these pistons move forward in concert, the main piston 117 reaching the forward limit, at which it stops, at which point a switching valve is switched so as to connect the front supply/discharge path 118 and the rear supply/discharge path 119 with the tank, thereby enabling the fluid locked condition with the die closed.
The above is the operating sequence of the fluid cylinder of Japanese Patent No. 2623075, during which process the cylinder chambers indicated as 150 and 161 in FIG. 13 also expand and contract, although there is absolutely no teaching therein of measures taken with respect to the increase and decrease of pressure of the cylinder chambers 150 and 151, which remains unclear.
In the above-described fluid cylinder according to the prior art, although there is indeed the achievement of a desired operation of a piston rod by a cylinder used for die drive in a die-cast machine or the like, as is clear from FIG. 13 as well, there is the need to form the complex passageways 118, 119, 136, and 137 within the cylinder casing 113 and the large-diameter piston 127 and, because the front opening/closing valve 135 and rear opening/closing valve 136 are substantially constitutional requirements for executing the above-noted operating sequence, it is also necessary to form the pilot passageways 138 and 145 within the cylinder case 113.
Therefore, it is necessary to make the wall thickness of the cylinder casing of the cylinder itself excessively thick and, because it is always important that this type of fluid cylinder be made small and light in order to build it into a die-casting machine, it was impossible to meet this requirement sufficiently.
Additionally, when a large number of flow paths are formed in the cylinder casing 113, for example, there is an inevitably large number of seal locations and, considering the need for this type of fluid cylinder to operate under severe conditions of high temperature and high pressure, this fact alone brings with it the problem of a commensurate increase in failures other problems and a decrease in reliability.
Additionally, while the front opening/closing valve 135 and rear opening/closing valve 126 are provided externally at the front and rear port parts, this results in a commensurate increase in the number of components, thereby aggravating the above-noted problems, while raising the number of forming steps and leading to an increase the cost of manufacture.
Accordingly, it is an object of the present invention to provide a cylinder apparatus with a fluid cylinder for use in die drive, having an extremely simple configuration, while providing a structure that stably executes the above-noted desired operational sequence, thereby solving the above-noted problems.